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<head>
  <title>Test for High Resolution Timer</title>
  <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
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<body>
  <script>
    ok(window.performance, "Performance object should exist.");
    ok(typeof window.performance.now == 'function', "Performance object should have a 'now' method.");
    var n = window.performance.now(), d = Date.now();
    ok(n >= 0, "The value of now() should be equal to or greater than 0.");
    ok(window.performance.now() >= n, "The value of now() should monotonically increase.");
    SimpleTest.waitForExplicitFinish();
    SimpleTest.requestFlakyTimeout("untriaged");

    // The spec says performance.now() should have micro-second resolution, but allows 1ms if the platform doesn't support it.
    // Our implementation does provide micro-second resolution, except for windows XP combined with some HW properties
    // where we can't use QueryPerformanceCounters (see comments at mozilla-central/xpcom/ds/TimeStamp_windows.cpp).
    // This XP-low-res case results in about 15ms resolutions, and can be identified when perf.now() returns only integers.
    //
    // Since setTimeout might return too early/late, our goal is that perf.now() changed within 2ms
    // (or 25ms for XP-low-res), rather than specific number of setTimeout(N) invocations.
    // See bug 749894 (intermittent failures of this test)
    var platformPossiblyLowRes = navigator.oscpu.indexOf("Windows NT 5.1") == 0; // XP only
    var allInts = (n % 1) == 0; // Indicator of limited HW resolution.
    var checks = 0;

    function checkAfterTimeout() {
      checks++;
      var d2 = Date.now();
      var n2 = window.performance.now();

      allInts = allInts && (n2 % 1) == 0;
      var lowResCounter = platformPossiblyLowRes && allInts;

      if ( n2 == n && checks < 50 && // 50 is just a failsafe. Our real goals are 2ms or 25ms.
           ( (d2 - d) < 2 // The spec allows 1ms resolution. We allow up to measured 2ms to ellapse.
             ||
             lowResCounter &&
             (d2 - d) < 25
           )
         ) {
        setTimeout(checkAfterTimeout, 1);
        return;
      }

      // Loose spec: 1ms resolution, or 15ms resolution for the XP-low-res case.
      // We shouldn't test that dt is actually within 2/25ms since the iterations break if it isn't, and timeout could be late.
      ok(n2 > n, "Loose - the value of now() should increase within 2ms (or 25ms if low-res counter) (delta now(): " + (n2 - n) + " ms).");

      // Strict spec: if it's not the XP-low-res case, while the spec allows 1ms resolution, it prefers microseconds, which we provide.
      // Since the fastest setTimeout return which I observed was ~500 microseconds, a microseconds counter should change in 1 iteretion.
      ok(n2 > n && (lowResCounter || checks == 1),
         "Strict - [if high-res counter] the value of now() should increase after one setTimeout (hi-res: " + (!lowResCounter) +
                                                                                                  ", iters: " + checks +
                                                                                                  ", dt: " + (d2 - d) +
                                                                                                  ", now(): " + n2 + ").");
      SimpleTest.finish();
    };
    setTimeout(checkAfterTimeout, 1);
  </script>
</body>
</html>
